Concerning the fact that regarding causes of congenital visual impairment or visual impairment occurring during the first years of life, especially on the aetiology many problems have never been resolved, on instigation of The Netherlands a "Committee for the special study of severe visual impairment in children" has been founded by the International Association for Prevention of Blindness. The intention was that provisionally in this committee only 5 small West European countries should be represented, having more or less the same social and hygienic conditions, so that one could expect that comparison of the gained information in these countries should give some results concerning the aetiology. The contributing countries were: Belgium, Denmark, Sweden, Norway, and The Netherlands. For this purpose criteria for definition of severe visual impairment, a questionnaire and a codinglist were drawn up. The classification scheme of causes of blindness and partial sightedness of the I.A.P.B. was utilized for answering the questions "by site and type and by aetiology" of the eye affections. The total number of children who were involved in the investigation was 4306. The investigation confirmed that heredity still occupies the first place in the aetiology of the congenital severe visual impairment. Moreover, the investigation could prove that besides the already known role of rubella, toxoplasmosis and dysoxygenation, probably also other affections occuring during pregnancy, prematurity, and too low birth weight (dysmaturity) and birth injuries, like asphyxia of the new-born child, are of great importance. Probably there is a correlation with certain eye affections (cataracta congenita and optic nerve atrophy). Attention is paid to the possibilities of prevention. From the results it appears that a renewed investigation is necessary where one should have to dispose of more and especially more reliable information concerning pregnancy and delivery. Suggestions in this direction are given.